PREFAGE ix 



intestine. Observations such as these are continually producing changes 

 in our outlook, so that, however quickly a book is produced, it is bound 

 to be out of date in certain respects when it appears. Nevertheless, the 

 greater part of the information which will be found on its pages is well 

 established, and will be lasting, so that it is sincerely hoped that the 

 two volumes will provide a reliable record of our knowledge up to the 

 beginning of 1926. 



As the study of spirochaetes is intimately related to that of the Pro- 

 tozoa, especially in connection with blood w^ork, a section is devoted to 

 their consideration, though it is definitely maintained that they are not 

 Protozoa. 



Many Protozoa which have affinities with those which produce diseases 

 in man and domestic animals have been found in the blood of other 

 vertebrates and in the intestines of invertebrates. A worker who dis- 

 covers such an organism has considerable difficulty in ascertaining if it 

 has been previously noted. To meet this difficulty a host list of the 

 blood-inhabiting parasites of vertebrates and one of the flagellates of 

 invertebrates have been compiled, and it is hoped they will be useful 

 references. 



As difficulties associated with nomenclature, the accuracy of which 

 is of such importance, are constantly occurring, the International Rules 

 of Zoological Nomenclature, which many workers have little opportunity 

 of consulting, have been included. 



The practical side of Protozoology has been constantly kept in mind, 

 as well as the difficulties which beset the path of those engaged in its 

 study. A special section deals with methods of investigations. This 

 is not intended to be a complete account, but merely a guide for the use 

 of those who already have a working knowledge of laboratory technique. 



Authorities for all statements made in the text have been given, and 

 the exact references will be found in the list of publications at the end 

 of the book. Practically all these have been consulted in the original, 

 and with very few exceptions every reference has been verified. The 

 greater part of this laborious work has been carried out by Miss I. M. 

 Bellis, Librarian to the Wellcome Bureau of Scientific Research, whose 

 knowledge of languages and scientific publications has been invaluable. 

 The writer is glad to have this opportunity of acknowledging his in- 

 debtedness to her for the great care she has taken with this and many 

 other parts of the work. The writer has constantly had the assistance of 

 Mr. Cecil Hoare, Protozoologist to the Wellcome Bureau of Scientific 

 Research. Many intricate questions have been discussed with him, and 

 his sound judgment, together with his careful and critical reading of 

 the proofs, has been a great asset. For many of the drawings, both 



